Several reasons or failures or electrical conditions may lead to a requirement to disconnect a wind power plant comprising plural wind turbines from the utility grid to which under normal conditions electric energy is supplied from the wind power plant. The failure may have occurred outside the wind power plant and may involve electrical conditions at a point of interconnection (where the plural wind turbines are connected to the utility grid) which results in disconnection of the plural wind turbines from the utility grid. For example, lightning, phase to phase short, ground fault or other protection trip resulting in the wind power plant being disconnected. Other examples could be routine maintenance on the wind power plant infrastructure or electrical faults inside the wind power plant.
After the failure or fault has been remedied, the wind power plant including the plural wind turbines need to be reconnected to the utility grid. In a conventional procedure, when power to a large wind power plant is restored after a power outage, it has been observed that the inrush-current may be very large and may result in difficulty complying with grid interconnection requirements or increase the rating of some portion of the infrastructure resulting in higher installation cost.
There may be a need for a method and for a system of coupling (or reconnecting) plural wind turbines to a utility grid after the wind turbines have been disconnected from the utility grid, wherein a stability of the utility grid, in particular regarding nominal values of voltage, reactive power, frequency, flicker etc., may be improved, or reached with a cheaper infrastructure.